Donkeys are not kosher, since they neither chew their cud nor have split hooves.

It is interesting, however, that donkey is the single non-kosher animal whose firstborn is considered holy. Now, in the case of a kosher animal, such as a sheep or goats, the firstborn was sacrificed in the Holy Temple and then eaten by the Kohanim (priests). Since donkeys are not kosher and they cannot be sacrificed in the Temple, what should be done with their firstborn? Scripture tells us that the firstborn donkey is exchanged for a lamb.1

Why is the donkey singled out? The Talmud explains that it is a gezerat hakatuv, a Scriptural decree with no reason provided. It then suggests that it is because donkeys were used to carry out the riches of Egypt during the Exodus.2